How low will 3D Printer Prices drop?

[Feign]

I know there are several out there already for under $300

There is pretty much just one and it has had some serious quality control issues.

Unless by 'out there' you mean 'in development', in which case there's a space ride ticket out there I could sell you.
In the next two years there will be three or four printers under $300 and maybe, just maybe one or two will be worth the effort of buying. The only attempt at a $100 printer kit is the Peachy, and even when development is done, it'll still most likely be a kit for the technically savvy.

Widespread printers under $300 will be five or more years off, and fully assembled 3D printers under $100 are eight or more years out (and the way things are going, might end up being measured in a different currency entirely by then.)